Revert "serial: 8250_exar: Set missing rs485_supported flag"

This reverts commit 00f09825 which is
commit 0c2a5f47 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I8753cedb8cc8783030a376a32a28137267949144
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>